Stocking knitting and knitting machines are usually provided with a cutting unit. This unit is intended to cut the yarn or yarns when they must be removed from the knitting though maintaining them in a position to be picked up again by the needles with an appropriate movement of the yarn guides and subsequently knitted. Also associated with the cutting unit are devices for locking the adjacent yarns by pneumatic openings to hold back the yarns proper until they will be taken up again by the needles.
One problem with the prior-art yarn-locking devices is that they do not effectively hold back the yarns, especially if they are elastic yarns; therefore, they tend to easily miss even the pneumatic openings. Another problem of the prior-art yarn-locking devices is that they do not always ensure that the yarns removed from the knitting will maintain a suitable position for their certain picking up again by the needles.